Underwater excavation apparatus

ABSTRACT

There is disclosed an excavation apparatus ( 5 ), such as an underwater excavation apparatus, having means for producing, in use, at least one vortex, spiral or turbulent flow in a laminar flow of fluid, e.g. water. The excavation apparatus ( 5 ) comprises a rotor ( 10 ) having a rotor rotation axis (A), wherein, in use, flow of fluid past or across the rotor ( 10 ) is at a first angle (a) from the axis of rotation (A). The excavation apparatus ( 5 ) comprises the rotor ( 5 ) and means or an arrangement for dampening reactive torque on the apparatus ( 5 ) caused by rotation of the rotor ( 10 ), in use. The turbulent flow is provided within, such as within a (transverse) cross-section, of the laminar flow.

CROSS REFERENCE TO RELATED APPLICATIONS

This U.S. utility patent application is a divisional of U.S. applicationSer. No. 16/327,822 filed Feb. 23, 2019, which is a U.S. national stageapplication of PCT Application No. PCT/GB2017/052490, filed on Aug. 23,2017, which claims priority from GB Patent Application Nos. 1702866.3filed on Feb. 22, 2017 and 1614460.2 filed Aug. 24, 2016, the contentsof which are incorporated herein by reference in their entireties.

FIELD OF INVENTION

This invention relates to an excavation apparatus, and in particular,though not exclusively, to an underwater (e.g. subsea) excavationapparatus. The invention also relates to an excavation system, device ortool, such as an underwater excavation system, device or tool, and to amethod of excavation, such as underwater excavation.

The invention also pertains to an underwater excavation apparatus orsystem comprising means for disturbing soil or soils or the like of aseabed, ocean floor, lake bed, river bed or the like, e.g. fordisturbing relatively firm soils.

BACKGROUND TO INVENTION

Mass flow excavators operate by directing a flow of high volume fluidunder low pressure at a seabed to displace seabed material. This is incontradistinction to jet type apparatus which direct a flow of lowvolume fluid under high pressure at the seabed. A mass flow excavator istypically tethered from a vessel by means of a crane wire, which is usedto lower and retrieve the excavator, and to maintain the excavator at agiven distance from the area/seabed or structure requiring excavation,such as a subsea oil or gas pipeline. In order to control theexcavation, sonar detection means can be used to allow the excavatoroperator to view the excavation in real time. Cameras and metaldetection means can also be used to assist the operator.

Underwater mass flow excavation apparatus are known. For example, GB 2297 777 A and WO 98/27286, also by a number of the present Inventors,the contents of which are incorporated herein by reference.

Mass flow excavation is a means of creating cavities in the seabed withrelatively low pressure(s) (Kilopascals, KPa), e.g. sand and/orpre-loosened or disturbed material. The mass flow excavation may beassisted by a mechanical means or high pressure jetting means foragitating the seabed. These ancillary means of cutting the seabed thenrely on mass flow excavation means to remove and disperse the seabedmaterial. Mass flow excavators typically comprise a hollow body housingand at least one impeller or rotor provided within the housing whichdraws fluid into the housing and directs the fluid out of the housingtowards the seabed.

Known mass flow excavators comprise impellers designed to draw in largevolumes of fluid and to discharge the fluid at relatively low speed andlow pressure—typically less than 6 m/s and less than 25 KPa. Due to therelatively low pressure and low fluid flow speed of mass flowexcavation, many passes may be required to effectively excavate an area,as with each pass only a limited penetration of the seabed may beachieved. It is a further characteristic of mass flow excavation thattrenches created in the seabed may be wide but shallow. This is becausethe mass flow excavator may first move looser material on the surfacedue to pressure limitations before penetrating firmer materialunderneath, creating a wide and ill-defined or uncontrolled excavationprofile.

Further, mass flow excavation apparatus are primarily suitable forexcavation by directing fluid at the seabed, but due to the low pressurenature of the apparatus, such are of limited use in the collection andremoval of seabed material by suction. Thus after the mass flow devicehas disturbed the seabed material a separate tool—such as a centrifugalpump—may require to be deployed to suck up and remove the material.

It is an object of at least one embodiment of at least one aspect of thepresent invention to obviate or mitigate one or more problems ordisadvantages in the prior art.

It is an object of at least one aspect of at least one embodiment of thepresent invention to provide a means to address a desire of excavatingin a relatively controlled and rapid manner with well-defined seabedexcavation profiles.

To distinguish from “mass flow” the term “controlled flow” ishereinafter used in connection with excavation with the presentinvention which may be configured to produce and/or direct a flow offluid at a pressure of typically around 35 to 120 KPa and volume flow oftypically around 1 m³/S to 8 m³/S. In contrast to mass flow devices, thehigher pressure capability of the controlled flow device makes thecontrolled flow device suitable for excavation in both excavation (e.g.jetting) mode and also in suction mode where the device may be used forcollection and transportation of seabed material away from an excavationsite.

SUMMARY OF INVENTION First Aspect

According to a first aspect of the present invention there is providedan excavation apparatus, such as an underwater excavation apparatus,having means or an arrangement for producing, in use, at least onevortex or spiral in a flow of fluid, e.g. water.

The at least one vortex may comprise a plurality of vortexes (vortices)which together may comprise a closed shape, e.g. circular, oval,elliptical or the like.

The vortex producing means may herein be referred to as a vortexgenerator(s).

The vortex producing means may, in use, cause a spiraling movement offluid flowing out of or into the excavation apparatus.

The excavation apparatus may comprise at least one rotor or impeller,and preferably may comprise a (i.e. a single) rotor.

The excavation apparatus may comprise at least one stator, andpreferably may comprise a (i.e. a single) stator.

The excavation apparatus may comprise a housing or hollow body. Thehousing may comprise an inlet and an outlet. In a first mode ofoperation, e.g. an excavation mode, the outlet may be directed towardsor face an area or region to be excavated. In such mode the inlet may,at least in use, be provided higher than or above, e.g. directly above,the outlet. In an alternative or second mode of operation, e.g. suctionmode, the inlet may be directed towards or face an area or region whichhas been excavated and/or requires cleared. In such mode the inlet may,at least in use, be provided lower than or below, e.g. directly below,the outlet.

The rotor and/or the stator may be provided in the housing. The housingmay comprise an axis. The rotor and the stator may be arrangedcoaxially, e.g. upon the axis. Beneficially, the rotor may be providedproximal the inlet and the stator may be provided proximal the outlet orvice versa.

The vortex producing means may be provided in, on or adjacent theoutlet.

In one embodiment the vortex producing means may be provided on an innersurface of the housing. In an alternative embodiment the vortexproducing means may be provided on a body, e.g. within the housing, e.g.within the outlet of the housing. The body may be provided on thehousing axis, e.g. coaxially with the rotor and stator.

In one embodiment the vortex producing means may be provided on an outersurface of the body. In an alternative embodiment the vortex producingmeans may be provided on an inner surface of the body. In such case thebody may comprise a ring.

The body may be attached to the housing, e.g. by one or more bladeswhich may be circumferentially disposed.

The vortex generating means may comprise at least one pair, andpreferably a plurality of pairs, of vortex generating means.

One member of a pair may generate a vortex spiraling in one direction,while another member of said pair may generate a vortex spiraling inanother or counter direction.

The vortex generating means, e.g. pairs of vortex generating means, maybe circumferentially disposed, e.g. on the housing or body.

Beneficially there may be provided six (6) pairs of vortex generatingmeans.

Each vortex generating means may comprise a planar member or tooth, e.g.a triangular planar member. An edge of the planar member may be attachedto the housing or body.

Each planar member may be disposed on the housing or body such that saidedge of the planar member is disposed at an angle (e.g. acute angle)relative to the axis of the housing.

Planar members of each pair of vortex generating means may be disposedat opposing angles.

In use, e.g. in an excavation mode or in a suction mode, a fluid flowmay enter the inlet and exit the outlet. Vortexes produced by the vortexgenerating means may be provided within a cross-section of the saidfluid flow.

Second Aspect

According to a second aspect of the present invention there is providedan excavation apparatus, such as an underwater excavation apparatus,comprising a rotor having a rotor rotation axis, wherein, in use, flowof fluid past or across the rotor is at a first angle from the axis ofrotation.

This arrangement may be beneficial in allowing excavation and/or suctionmodes of the apparatus. In excavation and suction mode fluid may flowfrom an inlet to an outlet of the excavation apparatus.

In use, fluid flow past or across the rotor may be non-axial to the axisof rotation of the rotor.

The excavation apparatus may comprise a housing or hollow body. Thehousing may comprise an inlet and an outlet. In a first mode ofoperation, e.g. an excavation mode, the outlet may be directed towardsor face an area or region to be excavated. In such mode the inlet may,at least in use, be provided higher than or above, e.g. directly above,the outlet. In an alternative or second mode of operation, e.g. suctionmode, the inlet may be directed towards or face an area or region whichhas been excavated and/or requires cleared. In such mode the inlet may,at least in use, be provided lower than or below, e.g. directly below,the outlet.

The rotor may comprise a first body, e.g. a first cone member.

The first angle may diverge away from the axis in a direction away fromthe inlet and towards the outlet.

An apex of the rotor cone may face the inlet.

The rotor may comprise a plurality of impellers or blades, e.g. aerofoilblades, which may be disposed, e.g. circumferentially disposed, on therotor cone.

The excavation apparatus may further comprise a stator. The stator maybe coaxial with the rotor. The stator may be provided between the rotorand the outlet.

Row of fluid past or across the stator may be at a second angle from theaxis of rotation of the rotor.

The stator may comprise a second body, e.g. a second cone member.

The second angle may converge towards the axis in a direction away fromthe inlet and towards the outlet.

An apex of the stator may face the outlet.

The stator may comprise a plurality of impellers or blades, e.g.aerofoil blades, which may be disposed on the stator cone.

The first angle may be in the range of 45° to 55° preferably around 50°.

The second angle may be in the range of 5° to 15°, and preferably around10°.

Third Aspect

According to a third aspect of the present invention there is providedan excavation apparatus, such as an underwater excavation apparatus,comprising at least one rotor and means or an arrangement for dampeningreactive torque on the apparatus caused by rotation of the rotor, inuse.

Most preferably the torque dampening means does not comprise a secondrotor, e.g. a second rotor counter-rotating to the at least one (single)rotor.

The excavation apparatus may comprise at least one rotor. In beneficialembodiments the at least one rotor comprises a single rotor.

The excavation apparatus may comprise at least one stator. In beneficialembodiments the at least one stator comprises a single stator.

The excavation apparatus may comprise a housing or hollow body. Thehousing may comprise an inlet and an outlet. In a first mode ofoperation, e.g. an excavation mode, the outlet may be directed towardsor face an area or region to be excavated. In such mode the inlet may,at least in use, be provided higher than or above, e.g. directly above,the outlet. In an alternative or second mode of operation, e.g. suctionmode, the inlet may be directed towards or face an area or region whichhas been excavated and/or requires cleared. In such mode the inlet may,at least in use, be provided lower than or below, e.g. directly below,the outlet.

The rotor and/or the stator may be provided in the housing. The housingmay comprise an axis. The rotor and the stator may be arrangedcoaxially, e.g. upon the axis. The housing may be provided upon theaxis. The rotor may be provided proximal the inlet and the stator may beprovided proximal the outlet.

The rotor may comprise a first body, e.g. cone body, and a plurality ofblades, disposed on, e.g. circumferentially around, the first body.

The stator may comprise a second body, e.g. cone body, and a pluralityof further blades, disposed on, e.g. circumferentially around, thesecond body.

The torque dampening means may comprise or include the stator blades.

The stator blades may comprise a plurality of primary stator blades, andoptionally secondary or splitter blades provided between adjacent pairsof primary stator blades.

The torque dampening means may comprise or include one or moreanti-rotation vanes. The anti-rotation vanes may comprise aerofoils. Theanti-rotation vanes may be provided between the rotor and the outlet.The anti-rotation vanes may be provided between the stator and theoutlet.

The anti-rotation vanes may be provided at or adjacent the outlet.

The anti-rotation vanes may be provided within the housing, e.g.circumferentially disposed within the housing.

An outer end of each anti-rotation vane may be connected to an innersurface of the housing. An inner end of each anti-rotation vane may beconnected to an outer surface of a/the ring provided within the housing.

Fourth Aspect

According to a fourth aspect of the present invention there is providedan excavation apparatus, such as an underwater excavation apparatus,comprising means or an arrangement for producing a laminar fluid flowand means or an arrangement for producing a turbulent fluid flow orvortex or spiral fluid flow within, such as a (transverse) cross-sectionof, the laminar flow.

A flow direction of the turbulent flow may be substantially parallel toa flow direction of the laminar flow.

The flow direction of the laminar flow and/or flow direction of theturbulent flow may be substantially parallel to a longitudinal axis ofthe excavation apparatus.

The turbulent flow may comprise a closed shape within, such as within across-section of, the laminar flow.

The turbulent flow may comprise at least one vortex or spiral and maycomprise a plurality of vortexes (vortices) which together may comprisea closed shape, e.g. circular, oval, elliptical or the like.

The turbulent flow may be substantially central within the laminar flowand/or within an outlet of the apparatus.

The turbulent flow/vortex producing means may herein be referred to as avortex generator(s).

The turbulent flow/vortex producing means may, in use, cause a spiralingmovement of fluid flowing out of or into the excavation apparatus.

The excavation apparatus may comprise at least one rotor or impeller,and preferably may comprise a (i.e. a single) rotor.

The excavation apparatus may comprise at least one stator, andpreferably may comprise a (i.e. a single) stator.

The excavation apparatus may comprise a housing or hollow body. Thehousing may comprise an inlet and an outlet. In a first mode ofoperation, e.g. an excavation mode, the outlet may be directed towardsor face an area or region to be excavated. In such mode the inlet may,at least in use, be provided higher than or above, e.g. directly above,the outlet. In an alternative or second mode of operation, e.g. suctionmode, the inlet may be directed towards or face an area or region whichhas been excavated and/or requires cleared. In such mode the inlet may,at least in use, be provided lower than or below, e.g. directly below,the outlet.

The rotor and/or the stator may be provided in the housing. The housingmay comprise an axis which may comprise or be consistent with thelongitudinal axis of the excavation apparatus. The rotor and the statormay be arranged coaxially, e.g. upon the axis. Beneficially, the rotormay be provided proximal the inlet and the stator may be providedproximal the outlet or vice versa.

The turbulent flow/vortex producing means may be provided in, on oradjacent the outlet.

In one embodiment the vortex producing means may be provided on an innersurface of the housing. In an alternative embodiment the vortexproducing means may be provided on a body, e.g. within the housing, e.g.within the outlet of the housing. The body may be provided on thehousing axis, e.g. coaxially with the rotor and stator.

In one embodiment the turbulent flow/vortex producing means may beprovided on an outer surface of the body. In an alternative embodimentthe vortex producing means may be provided on an inner surface of thebody. In such case the body may comprise a ring.

The body may be attached to the housing, e.g. by one or more bladeswhich may be circumferentially disposed.

The turbulent flow/vortex generating means may comprise at least onepair, and preferably a plurality of pairs, of vortex generating means.

One member of a pair may generate a vortex spiraling in one direction,while another member of said pair may generate a vortex spiraling inanother or counter direction.

The turbulent flow/vortex generating means, e.g. pairs of turbulentflow/vortex generating means, may be circumferentially disposed, e.g. onthe housing or body.

Beneficially there may be provided six (6) pairs of turbulentflow/vortex generating means.

Each turbulent flow/vortex generating means may comprise a planar memberor tooth, e.g. a triangular planar member. An edge of the planar membermay be attached to the housing or body.

Each planar member may be disposed on the housing or body such that saidedge of the planar member is disposed at an angle (e.g. acute angle)relative to the axis of the housing.

Planar members of each pair of turbulent flow/vortex generating meansmay be disposed at opposing angles.

In use, e.g. in an excavation mode or in a suction mode, a fluid flowmay enter the inlet and exit the outlet. Vortexes produced by theturbulent flow/vortex generating means may be provided within across-section of the said fluid flow.

In any of the foregoing aspects the following may be provided.

An inside and/or an outside of the housing may diverge (from an inlet)towards the rotor.

An inside and/or an outside of the housing may converge (from thestator) towards the outlet.

The housing may be circumferentially symmetrical about the axis.

In preferred embodiments, in use, fluid flowing through or exiting theexcavation apparatus may typically have a total pressure of around 35 to120 KPa and a volume flow rate of 1 to 8 m³/S.

Further Aspects

According to a fifth aspect of the present invention there is providedan excavation system, device or tool, such as an underwater excavationsystem, device or tool, comprising at least one excavation apparatusaccording to the first, second, third or fourth aspects of the presentinvention.

According to a sixth aspect of the present invention there is provided amethod of excavation, such as underwater excavation, the methodcomprising:

providing at least one excavation apparatus according to the first,second, third or fourth aspects of the present invention;

excavating a location, region or area, such as an underwater location,region or area, using said excavation apparatus.

It should be understood that any features defined above in accordancewith any aspect of the present invention or below in relation to anyspecific embodiment of the invention may be utilised, either alone or incombination with any other feature defined in any other aspect orembodiment of the present invention.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the present invention will now be described by way ofexample only, with reference to the accompanying drawings, which are:

FIG. 1 a schematic diagram illustrating fluid flow through a hollow bodyof an excavation apparatus according to an embodiment of the presentinvention;

FIG. 2(a) a schematic view of stator blades;

FIG. 2(b) a schematic view of stator blades of an excavation apparatusaccording to an embodiment of the present invention;

FIG. 3 a schematic side view of anti-rotation vanes of an excavationapparatus according to an embodiment of the present invention;

FIG. 4 a further schematic side view of the anti-rotation vanes of FIG.3 ;

FIG. 5 a schematic side view of an excavation apparatus according to anembodiment of the present invention;

FIG. 6 a perspective view from below and to one side of an exit nozzleof the excavation apparatus of FIG. 5 ;

FIG. 7(a) a partial sectional side view of an excavation apparatusaccording to an embodiment of the present invention;

FIG. 7(b) a partial sectional side view of the excavation apparatus ofFIG. 7(a) to an enlarged scale;

FIG. 8 a perspective view from below and to one side of an exit nozzleor outlet of an excavation apparatus according to an embodiment of thepresent invention;

FIG. 9 a sectional view from above of the exit nozzle of the excavationapparatus of FIG. 8 ;

FIG. 10 a sectional side view of an excavation apparatus according to anembodiment of the present invention;

FIG. 11 a perspective view from above and to one side of a rotor of anexcavation apparatus according to an embodiment of the presentinvention;

FIG. 12 a perspective view from above and to one side of a stator of anexcavation apparatus according to an embodiment of the presentinvention.

FIG. 13 a cross-sectional side view of an exit nozzle of an excavationapparatus according to an embodiment of the present inventionillustrating laminar flow and turbulent flow exiting the exit nozzle, inuse; and

FIG. 14 a cross-sectional end view of the exit nozzle of the excavationapparatus of FIG. 13 illustrating the laminar flow and turbulent flowexiting the exit nozzle, in use.

DETAILED DESCRIPTION OF DRAWINGS PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described withreference to the accompanying drawings.

According to embodiments of the present invention there is provided anexcavation apparatus 5, such as an underwater excavation apparatus,comprising a rotor 10 having a rotor rotation axis A, wherein, in use,flow of fluid past or across the rotor 10 is at a first angle α from theaxis of rotation A.

This arrangement is beneficial in allowing excavation and/or suctionmodes of the apparatus 5. In excavation mode and suction mode, fluidflows from an inlet 25 to an outlet 30 of the excavation apparatus 5.

In use, fluid flow past or across the rotor 10 is non-axial to the axisof rotation A of the rotor 10.

The excavation apparatus 5 comprises a housing or hollow body 20. Thehousing 20 comprises inlet 25 and outlet 30. In a first mode ofoperation, e.g. excavation mode, the outlet 30 is directed towards orfaces an area or region to be excavated. In such mode the inlet 25 is,at least in use, typically provided higher than or above, e.g. directlyabove, the outlet 30. In an alternative or second mode of operation,e.g. suction mode, the inlet 25 is directed towards or faces an area orregion excavated and/or requires to be cleared. In such mode the inlet25, is at least in use, provided lower than or below, e.g. directlybelow, the outlet 30.

The rotor 10 comprises a first body 39, e.g. a first cone member. Thefirst angle α diverges away from the axis A in a direction away from theinlet 25 and towards the outlet 30. An apex of the rotor 10 faces theinlet 25. The rotor 10 comprises a plurality of impellers or blades 35,e.g. aerofoil blades, which are disposed, e.g. circumferentiallydisposed, on the rotor cone.

The excavation apparatus 5 further comprise a stator 15. The stator 15is coaxial with the rotor 10. The stator 15 is provided between therotor 10 and the outlet 30.

Row of fluid past or across the stator 15 is at a second angle β fromthe axis of rotation of the rotor 10. The stator 15 comprises a secondbody 40, e.g. a second cone member. The second angle β converges towardsthe axis A in a direction away from the inlet 25 and towards the outlet30.

An apex of the stator 15 faces the outlet 30. The stator 15 comprises aplurality of vanes or blades 45, e.g. aerofoil blades, which aredisposed on the stator cone.

The first angle α is in the range of 45° to 55°, and beneficially around50°.

The second angle β is in the range of 5° to 15°, and preferably around10°.

The excavation apparatus 5, such as an underwater excavation apparatus,comprises at least one rotor 10 and means or an arrangement fordampening reactive torque on the apparatus 5 caused by rotation of therotor 10, in use. Beneficially the at least one rotor 10 comprises asingle rotor 10. The torque dampening means does not comprise a secondrotor, e.g. second rotor counter-rotating to the at least one (single)rotor 10.

The excavation apparatus 5 comprises at least one rotor 10. Inbeneficial embodiments the at least one rotor 10 comprises a singlerotor 10.

The excavation apparatus 5 may comprise at least one stator 15. Inbeneficial embodiments the at least one stator 15 comprises a singlestator 15.

The excavation apparatus comprises a housing or hollow body 20. Thehousing 20 comprises inlet 25 and outlet 30. In a first mode ofoperation, e.g. excavation mode, the outlet 30 is directed towards orfaces an area or region to be excavated. In such mode the inlet 25, atleast in use, is typically provided above, e.g. directly above, theoutlet 30. In an alternative or second mode of operation, e.g. suctionmode, the inlet 25 is directed towards or faces an area or regionexcavated and/or requires to be cleared. In such mode the inlet 25, isat least in use, provided lower than or below, e.g. directly below, theoutlet 30.

The rotor 10 and/or the stator 15 are provided in the housing 20. Thehousing 20 comprises an axis. The rotor 10 and the stator 15 arearranged coaxially, e.g. upon the axis A. The housing 20 is providedupon the axis A. The rotor 10 is provided proximal the inlet 25 and thestator 15 is provided proximal the outlet 30. The rotor 10 comprises afirst body 39, e.g. cone body, and a plurality of blades 35, disposedon, e.g. circumferentially around, the first body 30.

The stator 15 comprises a second body 40, e.g. a further cone body, anda plurality of further blades 45, disposed on, e.g. circumferentiallyaround, the second body 40. The torque dampening means comprises orincludes the further blades 45. The stator blades 45 comprises aplurality of primary stator blades 46 and secondary or splitter blades47 provided between adjacent pairs of primary stator blades 46.

The torque dampening means comprise or include one or more anti-rotationvanes 50. The anti-rotation vanes 50 comprise aerofoils. Theanti-rotation vanes 50 are provided between the rotor 10 and the outlet30. The anti-rotation vanes 50 are provided between the stator 15 andthe outlet 30. The anti-rotation vanes 50 are provided at or adjacentthe outlet 30. The anti-rotation vanes 50 are provided within thehousing 20, e.g. circumferentially disposed within the housing 20.

An outer end of each anti-rotation vane 50 is connected to an innersurface of the housing 20. An inner end of each anti-rotation vane 50 isconnected to an outer surface of a ring 55 provided within the housing20.

An inside and/or an outside of the housing 20 diverges from the inlet 25towards the rotor 10. An inside and/or an outside of the housing 20converges from the stator 15 towards the outlet 30. The housing 20 iscircumferentially symmetrical about the axis.

In preferred embodiments the fluid flowing through or exiting theexcavation apparatus 5 typically has a pressure of around 35 to 120 KPaand a volume flow rate of 1 to 8 m³/S.

In the disclosed embodiment, the excavation apparatus 5, such as anunderwater excavation apparatus, has means or an arrangement 60 forproducing, in use, at least one vortex or spiral in a flow of fluid,e.g. water.

The at least one vortex can comprise a plurality of vortexes whichtogether can comprise a closed shape, e.g. circular, oval, elliptical orthe like. The vortex producing means 60 hereinafter can be referred toas a vortex generator(s). The vortex producing means 60, in use, cause aspiraling movement of fluid flowing out of or into the excavationapparatus 5. The excavation apparatus 5 comprises at least one rotor 10or impeller, and beneficially comprises a (i.e. a single) rotor 10. Theexcavation apparatus 5 comprises at least one stator 15, andbeneficially comprises a (i.e. a single) stator 15.

The excavation apparatus 5 comprises housing or hollow body 20. Thehousing 20 comprises inlet 25 and outlet 30. In a first mode ofoperation, e.g. excavation mode, the outlet 30 is directed towards orfaces an area or region to be excavated. In such mode the inlet, atleast in use, is provided above, e.g. directly above, the outlet 30. Inan alternative or second mode of operation, e.g. suction mode, the inlet25 is directed towards or faces an area or region excavated and/orrequires to be cleared. In such mode the inlet 25, is at least in use,provided lower than or below, e.g. directly below, the outlet 30.

The rotor 10 and/or the stator 15 is provided in the housing 20. Thehousing 20 comprises axis A. The rotor 10 and the stator 15 are arrangedcoaxially, e.g. upon the axis A. The rotor 10 is provided proximal theinlet 25 and the stator is provided proximal the outlet 30.

The vortex producing means 60 are provided in, on or adjacent the outlet30.

In one embodiment the vortex producing means 60 are provided on an innersurface of the housing 20. In an alternative embodiment the vortexproducing means 60 are provided on a body 65, e.g. within the housing20, e.g. within the outlet of the housing 20. The body 65 is provided onthe housing axis, e.g. coaxially with the rotor 10 and stator 15.

In one embodiment the vortex producing means 60 is provided on an outersurface of the body 65. In an alternative embodiment the vortexproducing means 60 is provided on an inner surface of a tube or hollowbody or can comprise a ring 55.

The vortex generating means 60 comprises at least one pair, andpreferably a plurality of pairs, of vortex generating means 60. Onemember of a pair generates a vortex spiraling in one direction, whileanother member of said pair generates a vortex spiraling in another orcounter direction. The vortex generating means 60, e.g. pairs of vortexgenerating means 60, are circumferentially disposed, e.g. on the housingor body 20. Beneficially there are provided six (6) pairs of vortexgenerating means 60.

Each vortex generating means 60 comprises a planar member or tooth, e.g.a triangular planar member. An edge of the planar member is attached tothe housing or body 20. Each planar member is disposed on the housing orbody 20 such that said edge of the planar member is disposed at an angle(e.g. acute angle) relative to the axis of the housing 20. Planarmembers of each pair of vortex generating means 60 are disposed atopposing angles.

In use, e.g. in an excavation mode, a fluid flow, exits the outlet 30.Vortexes produced by the vortex generating means 60 are provided withina cross-section of the said fluid flow.

The body 65 is attached to the housing 20, e.g. by one or more blades 50which are circumferentially disposed.

Laminar Flow/Turbulent Flow

Referring now to FIGS. 13 and 14 , according to embodiments of thepresent invention hereinbefore described, the excavation apparatus 5,such as an underwater excavation apparatus, comprises means or anarrangement for producing a laminar flow LF and means or an arrangementfor producing a turbulent flow TF or vortex or spiral flow, theturbulent flow being provided within the laminar flow LF. In thisexample the turbulent flow TF is provided within a cross-section(transverse cross-section) of the laminar flow LF.

The laminar flow LF is represented by arrows or dots, while theturbulent flow TF is represented by spiral/looped lines.

As can be seen from FIGS. 13 and 14 , a flow direction of the turbulentflow TF is substantially parallel to a flow direction of the laminarflow LF. Also, in this embodiment, the flow direction of the laminarflow LF and/or flow direction of the turbulent flow TF is/aresubstantially parallel to a longitudinal axis A of the excavationapparatus 5.

As can also be seen from FIGS. 13 and 14 , the turbulent flow TFcomprises a closed shape within a transverse cross-section of thelaminar flow LF, i.e. perpendicular to the flow direction. Also, in thisembodiment, the closed shape of the turbulent flow TF is substantiallycentred within the laminar flow LF and within the outlet 30.

Non-Axial Rotor Fluid Flow

Hydrodynamic performance of subsea flow excavation devices is determinedby factors such as:

-   -   internal shape of the hollow body (or housing or shroud) which        houses the impeller(s);    -   impeller design;    -   inlet and outlet design; and    -   use of guide vanes within the device.

Known mass flow devices typically house impellers within simple tubularforms of hollow body and are designed so that the impellers receive anddischarge the fluid with very little change of direction. See, forexample, GB 2 240 568 A (SILLS), GB 2 297 777 A (DIKKEN) and EP 1 007796 B1 (SUSMAN). In such prior art the impellers receive and dischargethe flow in a purely axial direction. In SUSMAN a change of directionoccurs after the fluid is discharged from the impeller. This axialconfiguration limits the amount of pressure that mass flow devices canimpart from the impeller into the fluid. To generate the higher fluidspeed and higher pressure within the controlled flow excavator accordingto the present invention, the impeller blade passages (formed by thecombination of impeller hub, impeller blades and impeller shroud) aswell as causing the fluid to rotate in a circumferential motion, alsodivert the fluid in a partly radial, partly axial direction (see FIG. 1). The partly radial nature of the impeller blades means that thecircumferential speed at the trailing edge of the blade is higher thanat the leading edge, thus imparting more kinetic energy into the fluidthan an axial impeller blade running at the same speed. Use of an‘aerofoil’ blade shape improves the hydrodynamic efficiency of the rotorblades.

In the controlled flow excavator according to the present invention thefluid leaves the impeller blades with a significant circumferentialvelocity, but also with both axial and radial velocities (see FIG. 1 ).Downstream of the impeller blade, the shape of the controlled flowapparatus flow passage, created by the housing and hub profiles, removesthe radial component of the flow by turning from a mixed radial andaxial direction to a purely axial direction. The fluid then travelsaxially but still with significant circumferential velocity and highkinetic energy at a relatively large radius. Blade passages of a statorsection remove the circumferential component of flow, converting some ofthe kinetic energy into pressure energy, and bring the fluid back to asmaller radius for ejection from the excavator in a relativelysmall-diameter concentrated flow or jet.

Reactive Torque Dampening

Another feature of typical mass flow excavators is the means by whichsuch cope with reactive torque transmitted from a drive mechanism intothe fluid passing through the device. The fluid in turn exerts an equaland opposing torque on the housing in the opposite direction (reactivetorque) which if not cancelled would make the body of the excavationdevice rotate in the opposite direction from the impeller, making theexcavation device unstable in use. SILLS uses a number of clump weightsdeployed with the device to counteract the reactive torque; DIKKEN andSUSMAN employ two counter rotating impellers so that each impellercounteracts the reaction of the other.

To avoid the need for complex devices to counteract reactive torque thecontrolled flow device of the invention provides guide vanes in a statorsection after an impeller to straighten fluid flow. Substantiallyremoving any circumferential motion or swirl caused by the impellerbefore the fluid exits the device substantially removes reactive torquefrom the excavator device. Because the fluid entering the stator hasrelatively high circumferential velocity compared to a conventional massflow excavator, the stator blades must turn the fluid throughsignificantly higher angles. This is achieved by a relatively highernumber of stator blades of a relatively longer length, with a relativelyhigher blade angle at the LE (leading edge), and the use of a splitterblade. The higher the blade angle at the LE, the higher is the blockagecaused by the blades, as shown in FIG. 2(a). This blockage effect limitsthe number of stator blades that can be efficiently used. As the fluidis turned, however, and the blades approach a more axial aspect, theeffective gap between the blades increases, reducing the effectivenessof the blades in straightening the flow. A splitter blade, which is asmall blade between each main blade, is therefore used to address thisproblem. The splitter blades increase the blading and hence help tostraighten the flow but do not increase the blockage to an unacceptablelevel because they are only present in the area where the blade anglesare smaller.

Particularly for operation in shallow water, it is important to seek tominimise a height of the controlled flow device, and while it would besimplest and less costly to house the stator blades in a purelycylindrical passage, i.e. one where the diameters do not change, inorder to minimise length the stator is housed in a converging section,i.e. one where the diameter is reducing, so that the tasks of firstlyremoving the circumferential velocity from the fluid and convertingkinetic into pressure energy, and secondly of bringing the fluid back toa smaller diameter for ejection through the nozzle, are combined in onesection.

The controlled flow excavator seeks to achieve stability in the water bycareful hydrodynamic stator blade design which seeks to ensure that whenthe excavation apparatus is running at designed operating parameters,the stator blades remove most if not all of the angular momentum fromthe fluid. Therefore, there is little residual reactive torque on thehousing of the excavator. However, at ‘off-design’ conditions, i.e.where the excavator apparatus is being used with significantly greateror smaller rotor speeds than ideal operating point, there may remain aresidual swirl in the fluid leaving the excavator apparatus. This meansthat the reactive torque may not have been fully eliminated by thestator blading. Anti-rotation blades attached to inside faces of nozzlesnear their outer diameter, as shown in FIG. 3 , help to reduce orminimise any residual reactive torque. These anti-rotation bladesconvert some or all of any remaining rotational velocity in the fluidinto torque in the opposite direction to the reactive torque which suchresidual swirl would produce. The anti-rotation blades are typicallypurely axial in profile with no camber (i.e. such are symmetrical abouta chord-line running through the blade), which together with the use ofan aerofoil profile induces lift in the desired direction regardless ofwhich direction the fluid is swirling in. Hence a torque on theexcavator housing is produced, in use, which partially or wholly offsetsthe reactive torque, as shown in FIG. 4 . To reduce manufacturing costs,the anti-rotation blades may also be plane flat plates, and may forexample be constructed from thick plate metal with, for example, roundedleading edges and sharpened trailing edges.

Vortex Generation

To further enhance the cutting capability of the controlled flowexcavation apparatus, the exit nozzle of the apparatus can comprise aseries of vortex generators to produce pairs of counter rotatingvortexes. Vortex generators can be of a half delta wing profile or canbe as simple as triangular or rectangular plates which are placed withinthe exit nozzle and are inclined to the flow to produce a strong vortexat the trailing edge of the vortex generator. The power of the vortexhitting the seabed locally weakens the area of the seabed to enablegreater penetration by the controlled flow.

By using counter rotating pairs each vortex helps contain and preservethe rotation of a neighbouring vortex(es) to produce more stablevortexes and avoid the creation of unwanted reactive torque as thetorque from each vortex is cancelled by its neighbour (see FIG. 9 ).

The anti-rotation vanes can also be used in conjunction with vortexgenerators as described below, particularly to locate and support a ringof vortex generating pairs.

The number of vortex pairs can be maximised by placement of the vortexgenerators at the outer diameter of the exit nozzle (see FIG. 6 ).

Such placement has potential to cause mixing of the exiting fluid fromthe controlled flow device and the body of fluid in which the device isbeing used, thereby slowing and causing dispersal of the controlledflow.

In an alternative embodiment (see FIGS. 7(a) and 7(b)), the vortexgenerators can be placed substantially in a centre of the exit nozzle,e.g. on a feature created to hold the vortex generators. However thisarrangement allows for only a more limited number of pairs of vortexgenerators.

In a further alternative embodiment (see FIG. 8 ), the vortex generatorscan be placed on a ring within the exit nozzle so that a greater numberof pairs may be used, while maintaining the vortexes wholly within thehigh speed flow from the controlled flow devices. Maintaining thevortexes wholly within the high speed flow helps to create stablevortexes. Supports which attach the vortex ring to the nozzle may be inthe form of anti-rotation blades as discussed above.

When used in suction mode the exit of the controlled flow apparatus canbe connected to a pipe or hose for transportation of a slurry mix offluid and seabed material (or spoil) away from the excavation site.Operating in this mode, the vortex generators in the exit of thecontrolled flow apparatus aid the transport of seabed material by mixingof the fluid which maintains the collected material in suspension.

It will be understood that in order to transport the excavated materialalong the transportation pipe that the ratio of seabed material to waterbeing transported should preferably not exceed a ratio of approximately15% to 20% solids to water. This ratio can be controlled by varying thepower supplied to the controlled flow apparatus.

To transport material over long distances, say 200 meters or further, itmay be necessary to add another controlled flow apparatus in serieseither directly coupled after the first controlled flow apparatus orsome distance along the transportation pipe.

It will be appreciated that the embodiments of the inventionhereinbefore described are given by way of example only, and are notmeant to be limiting of the invention in any way.

It will be appreciated that modifications may be made to the disclosedembodiments. For example, the turbulent means or vortex producing meansor vortex generator(s) may be provided on the anti-rotation vanes, e.g.on an inner edge(s) of the anti-rotation vanes.

What is claimed is:
 1. An excavation apparatus, comprising: at least onerotor; at least one stator comprising stator blades, the stator bladescomprising a plurality of larger primary stator blades and a pluralityof smaller secondary or splitter blades provided between adjacent pairsof the larger primary stator blades; and a torque dampening arrangementfor dampening reactive torque caused by rotation of the rotor, thetorque dampening arrangement comprising the stator blades.
 2. Theexcavation apparatus as claimed in claim 1, wherein the at least onerotor comprises a single rotor.
 3. The excavation apparatus as claimedin claim 1, wherein the torque dampening arrangement does not comprise asecond rotor.
 4. The excavation apparatus as claimed in claim 1, whereinthe torque dampening arrangement does not comprise a second rotorcounter-rotating to the at least one rotor.
 5. The excavation apparatusas claimed in claim 1, wherein the rotor comprises a first body and aplurality of rotor blades disposed on the first body.
 6. The excavationapparatus as claimed in claim 1, wherein the at least one statorcomprises a single stator.
 7. The excavation apparatus as claimed inclaim 6, wherein the at least one stator comprises a second body and thestator blades are disposed on the second body.
 8. The excavationapparatus as claimed in claim 1, further comprising a housing comprisinga hollow body, the housing comprising an inlet and an outlet.
 9. Theexcavation apparatus as claimed in claim 8, wherein the excavationapparatus is operable in an excavation mode, and in the excavation modethe outlet faces an area to be excavated and the inlet is provided abovethe outlet.
 10. The excavation apparatus as claimed in claim 8, whereinthe excavation apparatus is operable in a suction mode, and in thesuction mode the inlet faces an area which has been excavated and to becleared, and the inlet is provided below the outlet.
 11. The excavationapparatus as claimed in claim 8, wherein the rotor and the stator areprovided in the housing, the housing comprises an axis, the rotor andthe stator are arranged coaxially upon the axis, the housing is providedupon the axis, and the rotor is provided proximal the inlet and thestator is provided proximal the outlet.
 12. The excavation apparatus asclaimed in claim 1, wherein the torque dampening arrangement comprisesone or more anti-rotation vanes.
 13. The excavation apparatus as claimedin claim 12, wherein the one or more anti-rotation vanes compriseaerofoils.
 14. The excavation apparatus as claimed in claim 12, furthercomprising a housing comprising an inlet and an outlet, and wherein theone or more anti-rotation vanes are provided between the rotor and theoutlet, and the one or more anti-rotation vanes are provided between thestator and the outlet.
 15. The excavation apparatus as claimed in claim12, further comprising a housing comprising an inlet and an outlet, andwherein the one or more anti-rotation vanes are provided at or adjacentthe outlet.
 16. The excavation apparatus as claimed in claim 12, furthercomprising a housing having a hollow body, and wherein the one or moreanti-rotation vanes are provided within the housing.
 17. The excavationapparatus as claimed in claim 16, further comprising a ring providedwithin the housing and having an outer surface, wherein eachanti-rotation vane of the one or more anti-rotation vanes has an outerend that is connected to an inner surface of the housing, and whereineach anti-rotation vane of the one or more anti-rotation vanes has aninner end that is connected to the outer surface of the ring providedwithin the housing.
 18. An excavation apparatus comprising: a housingcomprising an inlet and an outlet; a rotor comprising a first body and aplurality of blades disposed on the first body; a stator comprising asecond body and a plurality of further blades disposed on the secondbody; and wherein the further blades comprise a plurality of largerprimary stator blades and smaller secondary or splitter blades providedbetween adjacent pairs of the plurality of larger primary stator blades.